2012 - Telecommunications Blog

A blog for mobile communications systems GSM , UMTS and LTE

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Monday, December 10, 2012

Call Setup and Call Handling in GSM

12/10/2012 04:37:00 AM 0
Call Setup and Call Handling in GSM

Call Setup


Different procedures are necessary depending on the initiating and terminating party:

  • Mobile Originating Call MOC: Call setup, which are initiated by an MS
  • Mobile Terminating Call MTC: Call setup, where an MS is the called party
  • Mobile Mobile Call MMC: Call setup between two mobile subscribers; MMC thus consists of the execution of a MOC and a MTC one after the other.
  • Mobile Internal Call MIC: a special case of MMC; both MSs are in the same MSC area, possibly even in the same cell.

 Mobile Originating Call MOC


1. Channel Request: The MS requests for the allocation of a dedicated signaling channel to perform the call setup.

2. After allocation of a signaling channel the request for MOC call setup, included the TMSI (IMSI) and the last LAI, is forwarded to the VLR

3. The VLR requests the AC via HLR for Triples (if necessary).

4. The VLR initiates Authentication, Cipher start, IMEI check (optional) and TMSI Re-allocation (optional).

5. If all this procedures have been successful, MS sends the Setup information (number of requested subscriber and detailed service description) to the MSC.

6. The MSC requests the VLR to check from the subscriber data whether the requested service an number can be handled (or if there are restrictions which do not allow further proceeding of the call setup)

7. If the VLR indicates that the call should be proceeded, the MSC commands the BSC to assign a Traffic Channel (i.e. resources for speech data transmission) to the MS

8. The BSC assigns a Traffic Channel TCH to the MS

9. The MSC sets up the connection to requested number (called party).

Remark: This MOC as well as the MTC described in the following describes only the principles of an MOC / MTC, not the detailed signaling flow.


Wednesday, April 18, 2012

VoIP protocols

4/18/2012 07:03:00 PM 2
VoIP protocols

Real-Time Transport Protocol (RTP)

RTP is used for transmitting audio and video packets between communicating computers. RTP is defined in RFC 3550 and "profiles", which specify how to packetize various audio and video codecs used in an RTP session, are defined in RFC 3551.

 RTP also addresses issues like packet order and provides mechanisms to help address delay and jitter. RTP was improved upon with the result being called Secure RTP which provides for encryption, authentication, and integrity of the audio and video packets transmitted between communicating devices.

H.323 

Developed by Study Group 16 of the ITU-T, H.323 is an umbrella standard encompassing
many subcomponent standards and annexes for transmitting multimedia (voice, video and data) across packet based networks. The two main subcomponent protocols are H.225 (call control), & H.245 (bearer control and capabilities exchange). H.225 consists of two main parts Q.931 (basic call control as used in ISDN networks) and RAS (Registration, Admission & Status).

H.323 also references other standards such as Real Time Protocol (RTP), G.xxx audio codecs, H.26x video codecs and T.120 real time data conferencing protocol.

SIP 

Developed by IETF, SIP is a mechanism to initiate, terminate & modify sessions in an IP
network. It uses a client / server architecture and the protocol is request-response based. It
enables personal mobility by tracking down users and delivering calls to an endpoint. It is a
lightweight, text-based protocol and reuses much of the construct of other internet protocols
such as HTTP and SMTP. SIP does not know about the underlying details of a session and relies on IETF protocol Session Description Protocol (SDP) to describe the session. It also interworks with other IETF protocols such as Megacop, RTP, RTSP, RSVP and SAP.


Both H.323 and SIP can be referred to as "intelligent endpoint protocols". What this means is that all of the intelligence required to locate the remote endpoint and to establish media streams between the local and remote device is an integral part of the protocol.

MGCP & Megacop/H.248 

There is another class of protocols which is complementary to H.323 and SIP referred to as "device control protocols". Those protocols are H.248 and MGCP. 

MGCP (Media Gateway Control Protocol) & Megacop/H.248 are relatively low level, master/slave protocols used between Call Agents and MGs. MGCP is not officially a standard but does exist as an informational RFC (RFC 3435). Megacop (IETF RFC 3015) & H.248 (ITU Rec.) are the same protocol developed by an IETF and ITU collaboration. It is derived from, and draws heavily from MGCP but adds several new enhancements.

Some service providers provide users with devices that implement H.248 or MGCP (or comparable protocols). In the core of the network, some device serving as the MGC provides the H.323 or SIP logic necessary to properly terminate VoIP calls around the world.

VoIP OSI Protocol Stack

Telecommunications Blog
Telecommunications Blog
I will explain QOS at next article .

Tuesday, April 10, 2012

What is VoIP ? - Introduction

4/10/2012 06:37:00 PM 4
What is VoIP ? - Introduction
What is VoIP

Around 1995 there was a revolutionary advancement in the way traditional voice traffic was
carried when voice, video and data were transmitted over a single ‘converged’ network. The
terms Voice Over IP (VoIP) and IP Telephony (IPT) were introduced to describe this method of
transport of voice signals as well as fax, DTMF tones, signalling traffic, and network management
traffic.


There are a number of protocols that may be employed in order to provide for VoIP communication services like :

  • SIP (Session Initiation Protocol) / RTP  (Real-Time Protocol)
  • IMS
  • H.323
  • H.248 / MGCP   ( comparable protocols )
  • Skype
VoIP can deliver voice, video, and data communications capabilities across a number of separate devices that work together, such as a mobile phone, a PC, and even an HD TV!.

You can enjoy VoIP sevice by using:
  1. An analog Telephone Adapter (ATA). It connected existing telephone jack, so you no need to change your old telephone hardware (system).
  2. Dedicated VoIP Phones. It is a Phones that create specially for IP/Packet Switch connection. Just plug this phone to your IP/internet network then you can enjoy VoIP service.
  3. A Softphone. It is a piece of software that installed at PC/Laptop to make you can enjoy VoIP service without dedicated hardware.
I will explain the protocols at the next article.

Wednesday, April 4, 2012

wimax network planning part 1

4/04/2012 01:00:00 PM 0
wimax network planning part 1
WiMAX (Worldwide Interoperability for Microwave Access) ( 802.16 - 802.16e ).WIMAX was developed to promote conformance and interoperability of the IEEE 802.16 standard (Wireless MAN).


we will learn how we can planning a wimax network but first we should know some important things .

 
Frequency Planning :

         • The frequency re-use is extremely important in reducing the interference and therefore increasing the capacity
         • Off-the-shelf frequency assignment do not minimize the deployment cost for your system.
         • An optimum frequency assignments can be applied by considering
         • Site locations
         • Power levels
         • User distribution
         • Spectrum availability
         • Geography and building characteristics.


Site Features Optimization

         • Number of antennas
         • Antenna directions
         • Antenna heights
         • Antenna powers
         • Antenna tilts
         • Number of channels
         • Frequency of channels
         • OFDM Parameters
         • Cyclic prefix
         • Number of subchannels
         • Subchannelization rates
         • Available modulations
         • Handover parameters
         • MIMO settings
         • Uplink / Downlink traffic ratios
         • Voice over IP related issues
         • Backhaul planning: fiber, minilink, HDSL…. capacity issues

Tuesday, March 27, 2012

what's 4G LTE-Advanced ?

3/27/2012 12:46:00 PM 0
what's 4G LTE-Advanced ?
The following essential landmark may be the standardization associated with LTE-Advanced (LTE Rel. 10 and beyond). To ensure that the actual mobile telecoms technologies will be able to come up with technology that could contend, you ought to make sure that brand new mobile technology are now being developed as well as created. This is actually the thinking at the rear of beginning the introduction of the brand new LTE-Advanced techniques, showing the actual technologies as well as building the actual LTE-Advanced requirements.


 While LTE's peak downlink speed is theoretically 300 Mbps, LTE-Advanced can ostensibly reach 1 Gbps but realistically would get only 100 Mbps in everyday use. LTE's uplink peak rates of 75 Mbps pale in comparison to LTE Advanced's 500 Mbps.

 Along with function beginning upon LTE-Advanced, numerous crucial specifications as well as crucial functions tend to be visiting lighting. While not set however within the specs, there are lots of higher level is designed for your brand new LTE-Advanced standards. These types of will have to become confirmed and far function continues to be carried out within the specs prior to they are almost all set. 

Presently a few of the primary heading is designed with regard to LTE-Advanced is visible beneath :-
  1. Peak data rates : downlink - 1 Gbps; uplink - 500 Mbps.
  2. Spectrum efficiency : 3 times greater than LTE.
  3. Peak spectrum efficiency : downlink - 30 bps/Hz; uplink - 15 bps/Hz.
  4. Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used.
  5. Latency : from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission.
  6. Cell edge user throughput to be twice that of LTE.
  7. Average user throughput to be 3 times that of LTE.
  8. Mobility : Same as that in LTE
  9. Compatibility : LTE-Advanced shall be capable of interworking with LTE and 3GPP legacy systems. 
LTE-Advanced would to be moving in numerous areas within 2013, along with suitable devices as well as gadgets growing together with this particular release.

    Thursday, March 22, 2012

    lte service providers

    3/22/2012 12:39:00 PM 0
    lte service providers
    This is a listing of businesses that are offering LTE technologies associated parts.




    4M Wireless designs and develops leading edge products to enable fourth generation mobile wireless based on the latest 3GPP Long Term Evolution (LTE) standards.


    1st to deliver 3GPP LTE design and style automation, sign generation and also sign analysis equipment, Agilent has recently included protocol test and network signaling analysis remedies.


    You can transform to an all IP LTE network to reduce your cost per megabit, increase capacity, and build a service-aware infrastructure for mobile broadband services.


    Altair Semiconductor is a leading developer of ultra-low power, small footprint and high performance 4G chips for LTE.


    Anritsu continues to be taking part positively within the 3GPP standardization of those brand new technology simultaneously because operating carefully using the main infra-structure, chip-set as well as fatal programmers.


    The Aricent Group is a global innovation and technology services company that helps clients imagine, commercialize, and evolve products and services for the connected world.
    As a member of the 3GPP, Aricent is committed to investing in developing and supporting solutions for Long Term Evolution (LTE).


    It provides a complete portfolio of software solutions for air interface monitoring, benchmarking, Mobile Applications, and analysis.


    Founded in 1986 in Berlin, AVM is one of the top two manufacturers of broadband devices in Europe.


    Bridgewater Systems, the global leader in intelligent broadband controls, provides pre-integrated solutions for mobile and converged operators to Transform their networks to 4G: WiMAX, LTE, and WiMAX to LTE.

    Wednesday, March 14, 2012

    what is 4G LTE cellular technology ?

    3/14/2012 02:20:00 PM 0
    what is 4G LTE cellular  technology ?
    Its full name is 3GPP Long Term Evolution for the Universal Mobile Telecommunications System, or 3GPP UMTS LTE for short. LTE (Long Term Evolution) is a wireless broadband technology designed to support roaming Internet access via cell phones and handheld devices.


    Where the current generation of mobile telecommunication networks are collectively known as 3G, LTE is marketed as 4G.


    Requirements :

    • Reduced cost per bit
    • Increased service provisioning – more services at lower cost with better user experience
    • Flexibility of use of existing and new frequency bands
    • Simplified architecture, Open interfaces
    • Allow for reasonable terminal power consumption

    LTE Specifications :



     LTE uses two different types of air interfaces (radio links), one for downlink (from tower to device), and one for uplink (from device to tower).For the downlink, LTE uses an OFDMA (orthogonal frequency division multiple access) air interface For the uplink (from device to tower), LTE uses the DFTS-OFDMA (discrete Fourier transform spread orthogonal frequency division multiple access) scheme of generating a SC-FDMA (single carrier frequency division multiple access) signal. 

    The major difference between the OFDMA signal for downlink and the SC-FDMA signal for uplink is that it uses a discrete Fourier transform function on the data to convert it into a form that can be used to transmit.

    Monday, February 27, 2012

    4G LTE air interface - Radio Frequency Aspects

    2/27/2012 08:50:00 AM 0
    4G LTE air interface - Radio Frequency Aspects
    LTE air interface adopts OFDMA (orthogonal frequency division multiple access) for the downlink and SC-FDMA (single-carrier frequency domain multiple access) for the uplink. It employs AMC (adaptive modulation and coding) as well as a number of optional MIMO (multiple-input multiple-output) antenna techniques and interference management methods for potential performance enhancements.

    Telecommunications Blog

    One of the first things to note about LTE is the integration between the Frequency Division Duplex (FDD) and Time Division Duplex (TDD) radio access modes. In the previous Universal Mobile Telephone System (UMTS) specifications, which also supported FDD and TDD, the RF specifications for the UE FDD, UE TDD, base station FDD and base station TDD modes were covered in separate documents.

    However, the early decision by 3GPP to fully integrate FDD and TDD modes for LTE has resulted in only one RF specification document each for the UE and the eNB. With the higher level of integration between the two modes, the effort required to support them should be less than it was in the past.

    Channel Bandwidths:

    LTE was designed from the start to support six different channel bandwidths. These are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. In addition to this the subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.

    Earlier versions of the specifications also supported 1.6 MHz and 3.2 MHz for interworking with LCR TDD, but these were removed when the LTE TDD frame structure was aligned with the FDD frame structure rather than the TD-SCDMA frame structure from UMTS.

    Saturday, February 4, 2012

    INTRODUCTION TO RF PLANNING 2

    2/04/2012 10:22:00 AM 1
    INTRODUCTION TO RF PLANNING 2
    TOOLS USED FOR RF PLANNING :

    • Network Planning Tool
    • CW Propagation Tool
    • Traffic Modeling Tool
    • Project Management Tool


    Network Planning Tool :

    • Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage,  doing  frequency planning  automatically,  creating neighbor lists etc.







    •  With a database that takes into account data such as terrain, clutter, and  antenna radiation patterns,  as  well  as  an intuitive  graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

           – Design wireless networks
           – Plan network expansions
           – Optimize network performance
           – Diagnose system problems
    • The major tools available in the market are Planet, Pegasos, Cell Cad.
    • Also many vendors have developed Planning tools of their  own like Netplan by Motorola, TEMS by Ericsson and so on.